Capabilities are a basic tool that is used all the time in real systems, often by people who don't even know they're using capabilities. Examples of capabilitie

Capabilities are a basic tool that is used all the time in real systems, often by people who don't even know they're using capabilities. Examples of capabilities in the real world include: - Unix file descriptors. - The "choose file" dialog used to upload files to web sites. - CSRF tokens. - "Anyone with the link can access" aka "unlisted" access control as implemented by many web apps. - OAuth2 access tokens. - Google Chrome's sandbox. - Mac OSX's app sandbox. - Sandstorm.io's sandbox. Of course, none of these are "theoretically pure" capabilities, but successful systems are never theoretically pure anything.